Can one provincial body expropriate land under its own legislation, e.g. where it is a provincial highway, and the land is aquired by the Ministry of Transportation, and then flipped to another provinical authority without any power to expropriate?

I.e. can a provinical body without power to expropriate do so through another provincial body or perhaps through a federal one where the highway is a provincial one but which may have federal uses?

Where could one look to find the answer, statue? BC Expropriation Act, BC Transportation Act, Local Govt Act?

Your posting raises an interesting legal issue regarding the validity of an expropriation. Generally speaking, a government agency cannot expropriate unless it has a statutory right to do so. However, it is necessary to first determine what the facts are. If you have encountered a specific situation where this issue might arise, legal advice should be obtained. It is too complex to resolve here.